OBJECTIVES: 1. Laser Doppler Velocimetry will be developed to provide absolute continuous measurements of the velocity of the red blood cells (RBC's) in individual vessels of the human retina. Maps of the RBC's velocity in the main arteries and veins and the range of velocity variation during the heart cycle will be established for the normal fundus and for the fundus of patients with various circulatory impairments. 2. A flow parameter, positive tau meson, which varies in proportion to the flow of the RBC's in a capillary bed will be measured from the optic nerve head microcirculation. The possibility of measuring positive tau meson from different depths of the optic nerve will be investigated by studying the wavelength dependence of this parameter. Pilot measurements of positive tau meson-values in patients with glaucoma will be obtained and compared to those from normal volunteers. 3. The diffusion of fluorescein in the optic nerve, as a test of the blood-brain barrier will be investigated in patients with diabetes and various degrees of diabetic retinopathy, in patients with chronic open-angle glaucoma and patients with ocular hypertension by means of the two-tracer dilution technique. In this technique, the passage of a diffusible dye (fluorescein) in a small region of the optic nerve is compared to that of a nondiffusible dye (indocyanine green). 4. A pilot study of the diffusion of fluorescein in the fovea of patients with diabetes will be performed using the two-tracer technique.